The present invention relates to communication equipment. More particularly, the present invention relates to a power passing inductor which is capable of passing a power signal without resulting in excessive loss or distortion of Radio Frequency (RF) signals above 900 MHz.
A fundamental goal of a cable television system is to deliver the best possible picture quality to its subscribers. To achieve this end, it is necessary to maintain a flat signal response of an appropriate power level. In most cable television systems, at least two signals are simultaneously transmitted through the same wire: a power signal at the frequency of 60 Hz, and data or RF signals commonly in the frequency range of 5 to 500 MHz. The recent industry trend has been to extend the range of RF signals up to and above 900 MHz. Absent appropriate internal circuitry, the 60 Hz power signal can interfere with the RF signals, thereby distorting picture quality.
When an electric component is inserted into a cable television system, the component will likely have some effect on the RF signals that are transmitted through the system. Often, the component will cause some loss or distortion of the RF signals. This effect is generally depicted by an "insertion loss trace," a graph of decibels (dB) versus frequency. On such a graph, a large swing in decibels indicates a large effect on the RF signal. Ideally, the insertion loss trace of any cable television component should fit into a 0.5 dB to 1 dB range. In order to maintain this flat signal response and corresponding good television reception, it is known that an inductor can be used to pass only the power signal while providing a theoretically high impedance to the RF signals. Existing power passing inductors, however, only work well up to about 900 MHz. Above 900 MHz, the interwinding capacitance of the inductors causes very wavy and unpredictable component signal responses.
The existing art discloses devices that operate satisfactorily with RF signals ranging from 5 to 900 MHz. For instance, U.S. Pat. Nos. 4,394,631 and 3,982,814 each operate only up to about 400 MHz. Another style device, which is unpatented but widely used, performs acceptably up to about 600 MHz. Above 600 MHz, its frequency response becomes wavy and unpredictable. U.S. Pat. No. 4,641,115 operates only up to about 900 MHz. After 900 MHz, a steep roll-off is seen in its insertion loss trace. Further, all of the above existing art differs in construction from the present invention, as is also true of U.S. Pat. Nos. 4,682,125; 3,980,975; 3,673,517; and 3,590,329.
As noted above, the recent industry trend has been to extend the upper frequency limit of cable television systems. In particular, the challenge has been to extend the operating frequency of cable television systems to above 900 MHz. Accordingly, a primary object of the invention is to provide a power passing inductor that is capable of passing the 60 Hz power signal without excessively interfering with RF circuitry operating at above 900 MHz, and preferably at frequencies on the order of 1 GHz.
Further objects and advantages of the present invention will become apparent in the following description.